Joints of high voltage cables are needed and therefore also known since the use of high voltage cables. Older high-voltage cables are of the fluid-filled type. This means, that the insulation and semiconductor layers in these cables are typically made of paper which is soaked with a fluid. The fluid is often oil, but gases are used, too. The fluid has a certain pressure and this pressure has to be controlled during the use of the cable. The installation of such cables, especially the joints, needs a lot of skill and time-consuming manual work as the insulation layers have to be removed at the cable end and have to be adapted and reconstructed for the joint.
In view of the above mentioned disadvantages of fluid filled cables there is a general trend to use solid-insulation cable instead of fluid-filled cables. Today, both cable types coexist. Therefore, there is a need for joints connecting both cable types in any combination.
US 2010/0101 835 A1 (Nexans) describes a joint between a fluid-filled cable and a solid-insulation cable and EP 2 403 087 A1 describes a joint between two fluid-filled cables. The connection on the fluid-filled cable side is in both documents the same. The fluid-filled cable is prepared in the following way: At the cable end, all insulating and semiconducting layers are removed from the conductor. Behind the bare conductor end, the insulation thickness is increased by adding more paper layers. For some distance along the cable, the fluid-tight metallic layer and the outer protection is removed. A part of the cable, starting shortly before the cable end and ending before the beginning of the metallic layer, is surrounded by a partition insulator in which a coupling electrode and a sleeve are moulded. The partition insulator is open at both ends and is at least partially covered with a conducting layer. A connector is placed in front of the cable conductor. Seals in the form of O-rings are places between the connector and the coupling electrodes. The sleeve is somehow connected to the metallic layer of the cable.
In the joint of EP 2 403 087 A1 the same construction is found at the second cable and the two connectors are held together by a metallic ring. In the joint of US 2010 0101 835 A1 the solid-insulation cable connector is surrounded by a filling piece. The details of the connection are not disclosed.
While the symmetry of the set-up of EP 2 403 087 A1 allows the use of a symmetrical body including deflectors and electrodes, the fluid-filled cable side has a significantly different outer diameter than the solid-insulation cable side in US 2010 0101 835 A1. Also the central electrode cannot be symmetric due to the connection.
Both of the joints described in the cited Nexans publications have disadvantages. Many connections between the elements of the joints have to be made in the field (on site). Since several elements have to be connected in a fluid-tight manner it is advisable to test the sealing. However, testing on site is in general difficult. Further more, the insulation of the fluid-filled cable needs to be increased locally in thickness which means that someone with the skill to form paper-insulations needs to be present. This is a skill which is not very common nowadays. At least in EP 2 403 087 A1, considering the way the connectors are connected, there is the risk of a sub-optimal electrical connection. The bulging shape of the sleeve part does not allow to use to standard slipping procedure for mounting the body onto the cable connection in the case of EP 2 403 087 A1. In the case of US 2010 0101 835 A1 the irregular shape of the aperture in the body prevents the use of standard bodies and the standard procedure to mount them.